1. Field of the Invention
This invention relates to a system for measuring the state of charge of a storage battery, and more particularly to a system for detecting the quantity of electricity of a storage battery to measure the state of charge thereof, the degree of charge thereof and the like.
2. Description of the Prior Art
Recently, a storage battery such as a nickel-cadmium accumulator, a lead-acid accumulator or the like has been frequently used as a power source for portable electrical apparatus. Such storage battery cannot constantly supply electricity of a desired level to a load for a long time, accordingly, it is required to charge a storage battery after supplying electricity to a load for a certain time. In order to continuously and normally operate an electrical apparatus, it is important to know, during the discharge of a storage battery, the quantity of electricity which the battery can further supply to a load to normally operate the load. For this purpose, equipment has been conventionally used which acts to measure the state of charge of a storage battery. Such conventional measuring equipment is generally constructed to directly measure the quantity of electricity charged into a storage battery or discharged therefrom to indicate the state of charge thereof. However, because the measurement of electrical quantity of a storage battery is greatly affected by temperature and charging efficiency thereof, and the like as well known in the art, it is substantially impossible to precisely determine the state of charge of a storage battery by measuring only the quantity of charging or discharging electricity thereof; thus, in the conventional measuring equipment, it has been required to correct measured electrical quantity in view of the influences due to temperature and charging efficiency of a storage battery, and the like.
However, such conventional measuring equipment as mentioned above is adapted to conduct such correction by analog-operation, the analog-operation being not capable of precisely accomplishing the correction; thus, the conventional measuring equipment does not allow the state of charge of a storage battery to be precisely detected. In addition, in order to precisely measure the state of charge of a storage battery, it is also required to correct measured values in view of the life variation thereof and the capacity variation thereof due to the self-discharge at the time when the storage battery is connected to neither a charger nor a load. However, the conventional measuring equipment of the type of analog-operation does not precisely accomplish such correction.